Cold-retreading of a truck tyre normally comprises removing the worn tread from the tyre, and applying a new tread to the tyre carcass. To apply a new tread to a carcass, a green-rubber intermediate strip or cushion and a pre-cured tread (PCT) strip are wound about the carcass; and the carcass is then inserted inside an autoclave and cured further to achieve optimum adhesion of the tread to the carcass by means of the bonding action of the cushion.
One example of a pre-cured tread strip ready for application to a tyre carcass is described in U.S. Pat. No. 5,277,727A1. And one example of a station for retreading a tyre using the above method is described in U.S. Pat. No. 6,368,439B1.
Before the green-rubber cushion is applied, the lateral surface of the carcass is sprayed with a liquid (so-called cement) with a green-rubber and normalheptane (or other organic solvent) base to assist adhesion of the green-rubber cushion to the carcass for retreading.
Applying cement, however, involves numerous drawbacks, in that, the cement being volatile and potentially highly pollutant, application calls for the use of a high-cost, bulky, insulated cementing booth (normally insulated with rock wool, which must be disposed of using appropriate, high-cost disposal methods); the cement is stored in drums, which must also be disposed of using appropriate, high-cost disposal methods; the presence of cement between the cushion and tread strip, i.e. of a heterogeneous material interposed between two layers of rubber, may impair performance of the retreaded tyre; and, finally, organic solvents such as those contained in the cement being highly pollutant, avoiding application of organic-solvent-based cement greatly reduces overall pollution of the tyre retreading process. In this connection, it is important to note that recent United Europe regulations (VOC 13/1999/EC) call for a 75% reduction in the use of organic solvents in industry by the year 2007.
U.S. Pat. No. 5,635,015A1 describes a tyre retreading method whereby, to avoid using cement, the green-rubber cushion is heated, before being wound onto the carcass, to improve adhesion of the green-rubber cushion, so cement is superfluous. Heating the green-rubber cushion, however, has been found to also soften it, thus making it more difficult to wind about the carcass.